Inhibition of Mcl-1 expression by citrate enhances the effect of Bcl-xL inhibitors on human ovarian carcinoma cells.

The inhibition of two major anti-apoptotic proteins, Bcl-xL and Mcl-1, appears essential to destroy chemoresistant cancer cells. We have studied their concomitant inhibition, using ABT 737 or siRNA targeting XL1 and citrate, a molecule which reduces the expression level of Mcl-1.Two cisplatin-chemoresistant ovarian cell lines (SKOV3 and IGROV1-R10) were exposed to ABT 737 or siRNA targeting XL1 and citrate at various individual concentrations, or combined. Cell proliferation, cell cycle repartition and nuclear staining with DAPI were recorded. Western blot analyses were performed to detect various proteins implied in apoptotic cell death pathways.Mcl-1 expression was barely reduced when cells were exposed to citrate alone, whereas a mild reduction was observed after ABT 737 treatment. Concomitant inhibition of Bcl-xL and Mcl-1 using ABT 737 or siXL1 associated with citrate was far more effective in inhibiting cell proliferation and inducing cell death than treatment alone.Given that few, if any, specific inhibitors of Mcl-1 are currently available, anti-glycolytic agents such as citrate could be tested in association with synthetic inhibitors of Bcl-xL.

siPGK1 sensitizes chemoresistant human ovarian cancer cell lines to cisplatin.

Enhanced glycolysis provides essential intermediates for cancer cell proliferation. Its inhibition could be a promising approach for destroying tumors, especially those developing in hypoxic conditions, which are presumably the most chemoresistant. In hypoxic cells, glycolysis provides the main part of ATP. Phosphoglycerate kinase-1 (PGK1) catalyzes a crucial reaction of glycolysis that reconstitutes the two molecules of ATP previously consumed. PGK1 inhibition could arrest growth or kill hypoxic and/or chemoresistant cells. We tested siPGK1 transfection in two human ovarian cancer cells lines of increasing chemoresistance, and showed that: Expression of PGK1 was significantly reduced and associated with blockade of cell growth in the G(1) phase; siPGK1 associated with cisplatin was more effective than cisplatin-alone at inhibiting proliferation of chemoresistant cells; siPGK1 -alone and -associated with cisplatin strongly increased expression of the BH3-only pro-apoptotic protein BCL-2 Interacting Mediator of cell death (BIM). PGK1 might be a key target for sensitizing chemoresistant cells to cisplatin.